Packagings of moulded pulp are used in a wide variety of fields and provide an environmental friendly packaging solution that is biodegradable. Products from moulded pulp are often used as protective packagings for consumer goods like for instance cellular phones, computer equipment, DVD players as well as other electronic consumer goods and other products that need a packaging protection. Furthermore moulded pulp objects can be used in the food industry as hamburger shells, cups for liquid content, dinner plates etc. Moreover moulded pulp objects can be used to make up structural cores of lightweight sandwich panels or other lightweight load bearing structures. The shape of these products is often complicated and in many cases they have a short expected time presence in the market. Furthermore the production series may be of relative small size, why a low production cost of the pulp mould is an advantage, as also fast and cost effective way of manufacturing a mould. Another aspect is the internal structural strength of the products. Conventional pulp moulded objects have often been limited to packaging materials since they have had a competitive disadvantage in relation to products for example made of plastic. Moreover it would be advantageous to provide a moulded pulp object with a smooth surface structure.
In traditional pulp moulding lines, se for example U.S. Pat. No. 6,210,531, there is a fibre containing slurry which is supplied to a moulding die, e.g. by means of vacuum. The fibres are contained by a wire mesh applied on the moulding surface of the moulding die and some of the water is sucked away through the moulding die commonly by adding a vacuum source at the bottom of the mould. Thereafter the moulding die is gently pressed towards a complementary female part and at the end of the pressing the vacuum in the moulding die can be replaced by a gentle blow of air and at the same time a vacuum is applied at the complementary inversed shape, thereby enforcing a transfer of the moulded pulp object to the complementary female part. In the next step the moulded pulp object is transferred to a conveyor belt that transfers the moulded pulp object into an oven for drying. Before the final drying of the moulded pulp object the solid content (as defined by ISO 287) according to this conventional method is in around 15-20% and afterwards the solid content is increased to 90-95%. Since the solid content is fairly low before entering the oven, the product has a tendency of altering its shape and size due to shrinkage forces and furthermore structural tensions are preserved in the product. And since the shape and size has altered during the drying process it is often necessary to “after press” the product thereby enforcing the preferred shape and size. This however creates distortions and deformations deficiencies in the resulting product. Furthermore the drying process consumes high amounts of energy.
Conventional pulp moulds which are used in the above described process are commonly constructed by using a main body covered by a wire mesh for the moulding surface. The wire mesh prevents fibres to be sucked out through the mould, but letting the water passing out. The main body is traditionally constructed by joining aluminium blocks containing several drilled holes for water passage and thereby achieving the preferred shape. The wire mesh is commonly added to the main body by means of welding. This is however complicated, time consuming and costly. Furthermore the grid from the wire mesh as well as the welding spots is often apparent in the surface structure of the resulting product giving an undesirable roughness in the final product. Furthermore the method of applying the wire mesh sets restrictions of the complexity of shapes for the moulding die making it impossible to form certain configurations in the shape.
In EP0559490 and EP0559491 a pulp moulding die preferably comprising glass beads to form a porous structure is presented, which also mentions that sintered particles can be used. A supporting layer with particles having average sizes between 1-10 mm is covered by a moulding layer with particles having average sizes between 0.2-1.0 mm. The principle behind this known technology is to provide a layer wherein water can be kept by means of capillary attraction and by using the kept water to backwash the moulding die in order to prevent the fibres from clogging the moulding die. This process is however complicated.
U.S. Pat. No. 6,451,235 shows an apparatus and a method for forming pulp moulded objects using two steps. The first steps wet-forms a pre fibrous object which in the second step is heated and pressed under a large pressure. The pulp mould is formed of solid metal having drilled drainage channels to evacuate fluid.
U.S. Pat. No. 5,603,808 presents a pulp mould where one embodiment shows a porous base structure covered by a metal coating comprising squared openings of 0.1 mm to 2.0 mm.
U.S. Pat. No. 6,582,562 discloses a pulp mould capable of withstanding high temperature.
All prior art methods related to the production of a pulp mould, including the above disclosed methods, present some disadvantage.